The present invention relates to a method for diagnosing the drive voltage for a piezoelectric actuator of an injector.
It is already known to use piezoelectrically driven injectors especially for a common-rail system. In this context, for initiating the injection procedure, the actuator is driven by an appropriate voltage, so that, based on the actuator""s change in length, a valve needle opens or closes the injection channel for the injection procedure. Because the injection medium, especially fuel for an internal combustion engine, is under high pressure, an exact duration for the opening and closing of the injector is necessary for the high-precision dosing of the injection quantity. Especially in injectors having a double-switching control valve, the problem arises that, due to the hysteresis behavior of the piezoelectric actuator, different voltages are required both for the closed position in the second seat as well as for the two xe2x80x9copenxe2x80x9d positions, in accordance with the switching direction. When the designated drive voltage of the actuator is not achieved, the result can be injection failure and therefore the uneven running of the engine, deterioration of exhaust emissions, and a decline in the comfort level.
In contrast, the method according to the present invention has the advantage that, by creating a tolerance band for each driving, a simple monitoring of the drive sequence is possible. It is especially advantageous that the tolerance bands are established taking into account system and injection conditions, so that a plausibility check can easily determine whether the desired drive voltage was present in the instantaneous injection cycle.
It is especially advantageous that the drive voltage is measured in the area of the actuator clamps, so that line interruptions right up to the actuator are detected simultaneously.
In injection systems having a multiple injection within one drive curve cycle, it is advantageous that the desired level of the drive voltage be monitored in each phase of the injection. In this manner, it is assured that each injection pulse is monitored and errors are easily recognized.
As a result of the symmetrical position of the tolerance bands around the setpoint values, it is assured that overcontrolling or undercontrolling is detected to the same degree.
In an injector having a double-switching control valve, there are for the individual switching states at least four voltage levels, which can be advantageously monitored in a simple manner without excessive cost.
When one of the predetermined tolerance bands is not reached, then an error exists, which can lead to a disruption in the injection, faulty injection, or engine damage.
In particular, by a multiple measuring and counting of the faulty measuring values, it is possible to carry out a fault analysis in a simple manner. For example, if a fault only occurs sporadically, then this can be evidence of a harmless disturbance. In this case, the counter is automatically reset.
Only if a fault occurs continuously can the conclusion be reached that the corresponding actuator, i.e., the corresponding injector, is not operating normally. In the case of a fault of this type, if there is a persisting deviation from regulation, then in an alternative configuration there can be a switchover from xe2x80x9cregulate drive voltagexe2x80x9d to xe2x80x9ccontrol drive voltage,xe2x80x9d in order to advantageously maintain at least emergency operation.
However, if the actuator itself should be defective, then it is switched off, so as not to damage the control unit having its end stage.
It is also advantageous to retain the most recently selected drive voltage, if the assumption can be made that, for example, the regulation is not operating as desired.
An error that arises is advantageously stored so that it may be reproduced, for example, in the workshop and the corresponding component part can be replaced.
In particular, to meet fuel economy and exhaust gas emission requirements, the application of the method seems advantageous in a common-rail injection system.